Fixing element

ABSTRACT

A fixing element comprising a fixing section and a tubular stamped or riveted section in which the stamped or riveted section enable the fixing element to be placed on a metal part and the fixing section enables an object to be placed on the metal part. A bearing surface on a transition region between the fixing section and the stamped or riveted section extends in a radial or conical manner and optionally has torsional fixing features. The tubular stamped or riveted section free front end has a conical cutting surface which is divergent on the radially inner side in the direction of the free front end area and a rounded impact and traction surface on the radially outer side. The cutting, impact and traction surfaces meet at an annular edge on the free front end of the stamped or riveted section and are shaped to prevent shavings from occurring.

The present invention relates to a fastener element having a fastenersection and a tubular piercing or rivet section with the piercing orrivet section being designed for the attachment of the fastener elementto a sheet metal part and with the fastener section being designed forthe attachment of an article to the sheet metal part, wherein, in theregion of the transition from the fastener section into the piercing orrivet section a radially or conically extending contact surface isprovided which optionally has features providing security againstrotation and the tubular piercing or rivet section ahs at its free endface on the radially inner side a conical inclined surface or cuttingsurface which diverges in the direction of the free end face and at theradially outer side a rounded punching an drawing surface, with theoblique surface or cutting surface and the pressing or drawing surfacemeeting at a annular end face edge at the free end face of the piercingor rivet section.

Fastener elements of this kind have been sold by the company ProfilVerbindungstechnik GmbH & Co. KG in various forms under the designationsSBF, SBK, RSF and RSK for many years. The elements themselves and alsothe method for the attachment of the elements and the die buttons thatare used are described in detail amongst other things in the Germanpatent DE 34 47 006 C2, DE 34 46 978 C2 and DE 38 35 566 C2.

Fastener elements of this kind are either introduced in self-piercingmanner into the sheet metal part so that the element has a piercing orrivet section. They can however also be introduced into pre-holed sheetmetals, with the pre-holing frequently taking place using a so-calledpreceding hole punch which pierces the sheet metal part directly beforeor during the attachment of the fastener element. This possibility onlyexists for fastener elements which are formed as hollow body elements,for example nut elements, because the hole punch has to pass through thefastener element.

The possibility also exists, likewise with hollow body elements, ofproviding them with a piercing and rivet section, of piercing the sheetmetal part with the piercing or rivet section and of removing the slugwhich arises and which is trapped inside the tube and rivet section byusing a follow up ejection pin.

Even when using the above-named element with pre-holed sheet metal partsthe piercing or riveting section has to provide a not inconsiderabledeformation work at the sheet metal part because it has to take care ofthe deformation of the sheet metal part to a tubular collar in theregion of the rivet connection. The piercing or rivet section issubsequently deformed radially outwardly around the free end face of thetubular collar in order to form a recess for the tubular collar ofU-shaped cross-section when viewed in a radial cross-section.

The requirements placed on the piercing or rivet section, irrespectiveof whether or not pre-holding is used, are thus to have adequatestability in order to be able to carry out the deformation which isrequired and, after the formation of the rivet bead, to achieve anadequate strength in the region of the rivet bead so that the strengthof the connection which is aimed at is ensured. This is required for thefirm attachment of an article to the sheet metal part. For a fastenerelement this moreover signifies that the strength of the piercing orrivet section must correspond to the strength class of the screw. Duringthe attachment of the fastener element to a sheet metal part thepiercing or rivet section may not buckle. On the other hand thedeformability must be present so that the piercing or rivet section canbe reshaped into the rivet bead which is of U-shape in radialcross-section.

These contrary demands lead to the radial wall thickness of the tubularpiercing or rivet section having to have a clear association with theeffective size of the fastener element. Under the designation “effectivesize of the fastener element” is to be understood the strength which isdemanded from the fastener element as such. If, for example, thefastener element is a bolt element then the effective size of thefastener section corresponds to the outer diameter of the threadcylinder, i.e. with a fastener element having a metric thread of 5 mmdiameter the effective size of the fastener section likewise amounts to5 mm. For a fastener element with a thread cylinder of 6 mm diameter theeffective size of the fastener section is 6 mm etc. If one is concernedwith a nut element the effective size is determined in precisely thesame manner, i.e. with a nut element of for example 8 mm internaldiameter the effective size of the fastener section is to be assumed tobe 8 mm. If, in contrast, it is a bolt element which is provided with ashaft part and which executes a journaling function or is designed toreceive a spring clip or to form a snap connection, then the outerdiameter of the shaft part counts as the effective size. For example,with a shaft part having a diameter of 10 mm, the effective size of thefastener section amounts to 10 mm.

The form of the conical cutting surface which diverges in the directionof the free end face and the form of the rounded pressing and drawingsurface provided at the radially outer side of the piercing or rivetsection are very precisely determined in the known fastener elements inorder to satisy the respective tasks.

In the known elements the cutting surface is formed as a conical surfacewhich has the hypotenuse of an imaginary right-angled triangle with alimb length perpendicular to the central longitudinal axis of thetubular piercing or rivet section of 0.2 mm to 0.3 mm, depending on theeffective size of the fastener section. The sense of this conicalcutting surface is on the one hand to compress the piercing slug in theradial direction when it is manufactured so that the piercing slug istrapped in the piercing or rivet section. This jamming stiffens thepiercing or rivet section during the subsequent deformation of the same,which is of advantage. On the other hand, the conical cutting surfaceserves to deflect the piercing or rivet section radially outwardly incollaboration with a central part of the die button. Both functions leadto a situation in which this cutting surface is made as broad aspossible from the point of view of its design.

The rounded pressing and drawing surface in the known elements has acentre of curvature which was placed on the inner wall of the piercingor rivet section, with the radius of curvature having a length whichcorresponds to the radial wall thickness of the tubular piercing orrivet section. In other respects the centre of curvature was so placedin the known elements that the rounded pressing and drawing surface runstangentially into the cylindrical outer surface of the tubular piercingor rivet section, with this rounded pressing and drawing surface at thefree end of the fastener element, which forms a annular end face edgewith the cutting surface at the free end face of the piercing or rivetsection, meeting this cutting surface in such a way that a tangent tothe rounded pressing and drawing surface at the annular end face edgeforms an acute angle to the central longitudinal axis of the tubularpiercing or rivet section which is significantly less than 90°.

Even when the said fastener elements have been successfully used inpractice for many years they have a disadvantage, namely that theattachment of the elements, irrespective of whether it takes place withor without pre-holing, leads to the formation of small chips which, inthe course of time, stick in the region of the die buttons or elsewherein the tools that are used and can lead to jamming and deformations,also of the sheet metal parts which are being processed, which areentirely undesirable.

The cause for these small chips is extremely difficult to understandsince one cannot visualize the way the chips arise in a large press,because the working area consists of solid metal and there is nopossibility of providing so to say observation windows which wouldenable the manufacturing process to be observed without substantiallyimpairing the course of the manufacturing process.

The object of the present invention is to set forth a modified form offastener elements of the initially named kind which do not lead to theformation of chips, or only lead to the formation of chips to asubstantially lesser degree, without the attachment method which hasotherwise proved itself (with or without pre-holding) having to bechanged and without the technical values of the connections which areachieved deteriorating, and it should also be possible to continue touse the die button which have previously been used.

In order to satisfy this object provision is made in accordance with theinvention that the conical cutting surface forms the hypotenuse of animaginary right angled triangle with a limb length perpendicular to thecentral longitudinal axis of the tubular piercing or rivet section of0.10 mm±0.03 mm, that the radial wall thickness of the tubular piercingor rivet section is dimensioned as a function of the effective size ofthe fastener section; that the rounded pressing and drawing surface hasa radius of curvature which is 0.1 mm±0.03 mm smaller than therespective radial wall thickness and that the centre of curvature of therounded pressing and drawing surface lies on the surface of an imaginarycylinder parallel to the axis which extends away from the annular endface edge in the direction of the fastener section and is so positionedat a point along the piercing or riveting section on the surface of theimaginary axially parallel cylinder that a tangent to the roundedpressing and drawing surface stands perpendicular to the centrallongitudinal axis at the annular end face edge.

Especially preferred embodiments of the fastener element can be found inthe subordinate claims.

Despite the difficulties involved when observing the method it hasproved possible to ascertain that the chips have in principle threeorigins. On the one hand they arise when the sheet metal part is cutthrough. However they also arise when the sheet metal part is drawn intothe tubular collar and they furthermore arise during the rolling of thepiercing or rivet section into the recess of the die button around thedrawn tubular collar region.

It has furthermore been found, in accordance with the invention thatthrough a special shaping of the piercing or rivet section in the regionof the conical cutting surface and of the rounded pressing and drawingsurface the tendency to chip formation can be substantially reduced andthus the object of the invention can be satisfied.

The invention will be explained in more detail in the following withreference to the drawings in which are shown:

FIGS. 1 to 12 the Figures from the German patent 34 47 006 which showthe method for the attachment of the fastener elements to sheet metalparts in the known form, with both a bolt element and also a nut elementbeing shown and with an ejection pin being used with the nut element toremove the piercing slug,

FIGS. 13 to 18 the FIGS. 4, 5 and 7 to 10 of the German patent 34 46 978C2 which show the attachment of a nut element using a preceding holepunch,

FIGS. 19, 20 a fastener element in the form of a bolt element inaccordance with the present invention, and indeed in the form of an endview and a side view partly sectioned in the longitudinal direction and

FIGS. 21–24 the design of the piercing and rivet section in the region Aof FIG. 20 in dimensioned form for bolt elements for the diameters M5,M6, M8 and M10 respectively.

Since the FIGS. 1 to 12 and 13 to 18 have been taken from the Germanpatents DE 34 47 006 C2 and DE 34 46 978 C2 and are fully describedthere they will only be briefly described here by way of explanation,particularly since the method sequence is straightforwardly evident fromthe individual drawings.

The fastener element of FIG. 1 is a stud bolt element 150. This studbolt element 150 comprises a shaft part 154, shown here without thread,and a head part 152 with a radial flange and a tubular piercing andrivet section 156. In this embodiment the jacket wall 158 of the tubularpiercing and rivet section is substantially of circularly cylindricalshape and terminates in a rounded pressing and drawing edge 160 at thefree end face of the tubular piercing and rivet section.

The inner wall 164 of the piercing and rivet section is likewisesubstantially cylindrical in this embodiment and terminates in a conicalcutting surface 166 which meets the rounded pressing and drawing edge160 at a ring-like end face edge at the free end face of the piercingand rivet section.

As can be seen from FIG. 2 a sheet metal part 206 is supported in apress tool by means of a die button 180 and the fastener element 150 isso pressed against the sheet metal part 206 by means of a press tool inthe form of a plunger of a press that, as shown in FIG. 3, a piercingslug 216 arises and the sheet metal part is drawn into a tubular collar218 (FIG. 4). The piercing slug 216 is pressed inside the tubularpiercing and rivet section by a plunger projection 184 of the die buttonand the piercing and rivet section 156 is rolled as a result of therounded rolling surface 202 of the die button 180 radially outwardlyaround the free end face of the tubular collar 218 forward the formationof a rivet bead until the end position of FIG. 8 is reached.

FIG. 9 shows how a plurality of bolt elements can be introduced oneafter the other into a piercing head 472 of a press so that for eachstroke of the press one bolt element can be stamped into a new sheetmetal part and riveted to the latter. Even when FIG. 7 shows aparticular shape of the die button, this can also have the form of abody of rotation, i.e. the planar coining regions 220 shown in FIG. 7 donot have to be present.

The FIGS. 10 to 12 show that a nut element can be used instead of a boltelement and furthermore show how, in this embodiment, the nut element isadmittedly introduced in a self-piercing manner into the sheet metalpart 650, the piercing slug is however subsequently pressed out by meansof an ejection pin 642 and disposed of via a central passage 638 of thedie button 632.

The FIGS. 13 to 18 show how a nut element 600 can be inserted into asheet metal part 650 using a so-called preceding hole punch 122 whichserves for the pre-holing of the sheet metal part 650 so that thepiercing and riveting section has a pressing and drawing function here,but is not used for the piercing of the sheet metal part. Independentlyof the precise layout of the attachment method and of the fastenerelement used all elements shown are provided with a piercing or rivetsection, which is provided at its free end face with a conical inclinedsurface or cutting surface at the radially inner side and at theradially outer side with a rounded pressing and drawing edge, with therounded pressing and drawing edge meeting the conical inclined surfaceat a annular end face edge of the piercing and rivet section.

As explained above the present invention relates to a special design ofthe piercing and rivet section in the region of its free end face whichensures the avoidance of chips.

The fastener element of FIGS. 19 and 20 is a bolt element 700 with afastener section 702 and a tubular piercing or rivet section 704, withthe piercing or rivet section being designed for the attachment of thefastener element to a sheet metal part and with the fastener sectionbeing designed for the attachment of an article to the sheet metal part.In the region of the transition from the fastener section 702 into thepiercing and rivet section a radially extending contact surface 7–8formed on a flange part 706 is provided here which, in the specificexample, is provided with features providing security against rotationin the form of noses 710 and recesses 712. Features providing securityhas to transmit torques to the sheet metal part in operation, forexample when an article is to be secured to the sheet metal part bymeans of a nut screwed onto the fastener section 702, with a torquearising at the fastener element on a screwing on of the nut as a resultof friction and having to be taken up by the sheet metal part. Suchtorques also arise when the nut is removed and must likewise be carriedor transmitted by the connection between the fastener element and thesheet metal part.

The tubular piercing or rivet section has at its free end face 714 aconical cutting surface 716 at the radially inner side and a roundedpressing and drawing surface 718 at the radially outer side, with thecutting surface 716 and the pressing and drawing surface meeting at aannular end face edge 720 at the free end face of the piercing or rivetsection.

The tubular piercing or rivet section 704 has a right cylindrical outerwall 722 and a right cylindrical inner wall 724 which are both disposedconcentric to the central longitudinal axis 726 of the fastener element.

The design in accordance with the invention of the tubular piercing orrivet section 704 in the region of its free end face, i.e. at theposition where the detail A is indicated in FIG. 20 will now bedescribed with reference to FIG. 21 for a fastener element in accordancewith FIG. 20 with an effective size of the fastener section of 5 mm,i.e. the outer diameter of the fastener section 702 amounts to 5 mm.

One can see from FIG. 21 that the conical cutting surface 716, whenconsidered in the radial cross section, forms the hypotenuse of animaginary isosceles right-angled triangle the equal length sides ofwhich are designed with the reference numerals 717, 719. The limb 717corresponds to the imaginary continuation of the inner wall 724 of thepiercing or rivet section 704 from the start of the oblique surface orinclined surface 716 up to the point of intersection with the imaginaryradius which goes from the annular end face edge 720 to the longitudinalaxis 726, with the section of the radius from the annular end face edgeto the intersection point with the imaginary continuation of the innerwall 724 of the piercing or rivet section 704 forming the limb 719. Inthis example the limbs 717 and 719 each have a limb length of 0.1 mm,and this limb length can amount, in accordance with the invention to 0.1mm±0.3 mm. Since this is preferably an isosceles triangle, which ishowever not essential, the cone angle of the conical intersectionsurface related to the central longitudinal axis 726 is 90°. Thedistance between the annular end face edge 720 and the radially innerwall 724 of the tubular piercing or rivet section amounts likewise to0.1 mm (radial distance measured at the annular end face edge 720).

The radial wall thickness R of the tubular piercing or rivet sectionamounts, in this example of a bolt element of the size M5, to 1.25±0.05mm. The rounded pressing and drawing surface 718 has, in accordance witthe invention, a radius of curvature which is 0.1 mm (±0.03 mm) smallerthan the respective radial wall thickness R (in this example 1.25 mm).Furthermore the centre of curvature 727 of the (circularly) roundedpressing and drawing surface lies on the surface of an imaginary axiallyparallel cylinder 728 which extends away from the annular end face edge720 in the direction of the fastener section 702. Furthermore the centreof curvature 727 is so placed at a point along the piercing or rivetsection, at the surface of the imaginary axially parallel cylinder 728,that the tangent 730 to the rounded pressing and drawing surface 718 atthe transition into the annular end face edge 720 stands perpendicularto the central longitudinal axis of the tubular piercing or rivetsection 704, as is indicated at 723. Accordingly the height of thecentre of curvature 727 above the annular end face edge 720 is likewise1.15 mm corresponding to the radius of curvature of the rounded pressingand drawing surface 718.

As a result of the geometrical relationships this design of the free endof the piercing or rivet section 704 leads to the rounded piercing anddrawing surface 718 likewise running tangentially into the rightcylindrical wall of the tubular rivet section. This also applies to theembodiment of FIG. 22 which recites the correct dimensions for a boltelement in the size M6 in accordance with the invention where the radialwall thickness of the piercing or rivet section 704 likewise amounts to1.25 mm.

One can see however from the FIGS. 23 and 24 that the relationships witha bolt element of the size M8 or M10 are different, so that here atangent 732 to the rounded pressing and drawing surface 718 of thepiercing or rivet section 704 forms an acute angle with a generatrix 734of the circular cylindrical wall 722 of the piercing or rivet section704. It has been found, in accordance with the invention, that this factis not disturbing for the invention and also contributes to a reductionof the generation of chips.

Since the FIGS. 22, 23 and 24 correspond to FIG. 21, apart from thespecific dimensions it is not necessary to separately describe theseFigures. Instead of this the same reference numerals have been insertedinto the FIGS. 22, 23 and 24 as in FIG. 21 and the description of FIG.21 is to be considered representative for the FIGS. 22, 23 and 24. Alldimensions are contained in the drawings are recited in mm and can thusbe taken from the drawing without problem.

It is furthermore pointed out that the precise form of the free end faceof the piercing or rivet section 704 also applies for all fastenerelements which are covered by this application, including also elementswith the designation SBF, SBK, RSF and RSK and in all possibleapplications of the claimed fastener elements (including theabove-described applications as a bearing journal, or a clip receiver orfor the formation of a snap connection) and can also be used for thesetypes of element when the intention is to avoid chips.

In all embodiments all materials can be named as an example for thematerial of the functional elements which are used for the-existing SBF,SBK, RSF and RSK elements. Such materials include alloys which in thecontext of cold deformation achieve strength values of the class 8 inaccordance with the Iso standard, for example a 35B2 alloy in accordancewith DIN 1654. The so formed fastener elements are suitable amongstother things for all commercially available steel materials for drawingquality sheet metal parts and also for aluminium or its alloys.Aluminium alloys, in particular aluminium alloys of high strength canalso be used for the functional elements, for example AlMg5. Functionalelements of higher strength magnesium alloys such as for example AM50also come into question.

1. Fastener element (700) having a fastener section (702) and a tubularpiercing or rivet section (704) having a radially inner side, a radiallyouter side, a central longitudinal axis, and a radial wall thickness (R)with the piercing or rivet section being designed for the attachment ofthe fastener element to a sheet metal part and with the fastener sectionbeing designed for the attachment of an article to the sheet metal part,wherein, in a region of transition from the fastener section (702) intothe piercing or rivet section, a radially or conically extending contactsurface (708) is provided and the tubular piercing or rivet section hasat its free end face (714) on the radially inner side a conical inclinedsurface or cutting surface (716) which diverges in the direction of thefree end face and at the radially outer side a rounded pressing anddrawing surface (718), with the inclined surface or cutting surface(716) and the pressing and drawing surface (718) meeting at an annularend face edge (720) at the free end face of the piercing or rivetsection (704), characterized in that the conical inclined surface orcutting surface (716) forms an hypotenuse of an imaginary right angledtriangle with a limb length perpendicular to the central longitudinalaxis (726) of the tubular piercing or rivet section (204) of 0.10mm±0.03 mm, in that the radial wall thickness (R) of the tubularpiercing or rivet section (704) is dimensioned as a function of aneffective size of the fastener section; that the rounded pressing anddrawing surface (718) has a radius of curvature (r) which is 0.1 mm±0.03smaller than the respective radial wall thickness (R) and in that thecentre of curvature (727) of the rounded pressing and drawing surface(718) lies on the surface of an imaginary cylinider (728) parallel tothe central longitudinal axis which an imaginary cylinder's (728)surface, said cylinder parallel to an axis which extends away from theannular end face edge (720) in the direction of the fastener section(702) and is so positioned at a point along the piercing or rivetingsection (704) on the surface of the imaginary axially parallel cylinder(728) that a tangent (730) to the rounded pressing and drawing surface(718) stands perpendicular to the central longitudinal axis (726) at theannular end face edge (720).
 2. Fastener element in accordance withclaim 1, characterized in that the radial wall thickness (R) of thetubular piercing or rivet section (704) is dimensioned as follows as afunction of the effective size of the fastener section: size of 5 mmR=1.25±0.05 mm size of 6 mm R=1.25±0.05 mm size of 8 mm R=1.50±0.05 mmsize of 10 mm R=1.82±0.05 mm.
 3. Fastener element in accordance withclaim 1, characterized in that it is a bolt element and the fastenersection is provided with a thread cylinder, or can be provided with athread cylinder, said thread cylinder having an outer diameter whichforms the effective size of the fastener section.
 4. Fastener element inaccordance with claim 1, characterized in that the fastener section isrealized as a shaft part, with the outer diameter of the shaft partforming the effective size of the fastener section.
 5. Fastener elementin accordance with claim 1, characterized in that it is a nut element inwhich the fastener section has a bore which is provided with one of abore having a bore diameter and a bore having an internal thread1 withan outer diameter with the respective one of said bore diameter and saidouter diameter determining said effective size of said fastener section.6. Fastener element in accordance with claim 1, characterized in that itis a hollow element which has a bore for the reception of a rotatableshaft in the fastener section, said bore having a diameter whichdetermines the effective size of the fastener section.
 7. Fastenerelement in accordance with claim 1, characterized in that it is a hollowelement which has a bore adapted to receive a clip mounting, said borehaving a diameter which determines the effective size of the fastenersection.
 8. Fastener element in accordance with claim 1, characterizedin that the fastener section is realized as a shaft part to receive arotatable journal with the outer diameter of the shaft part forming theeffective size of the fastener section.
 9. Fastener element inaccordance with claim 1, characterized in that the fastener section iscapable of being provided with features of shape for the formation of asnap connection with the outer diameter of the shaft part forming theeffective size of the fastener section.
 10. Fastener element inaccordance with claim 1, characterized in that the fastener section iscapable of being provided with a mount for a spring clip with the outerdiameter of the shaft part forming the effective size of the fastenersection.
 11. Fastener element in accordance with claim 1, wherein theradially or conically extending contact surface (708) has features (710,712) providing security against rotation.